Generation 4 Double Battles have a couple of significant bugs with spread damage reduction.
1. On Showdown when a pokemon uses a spread attack move, all the damage calculations appear to be done at the start of the attack, however in generation 4 this is incorrect. On cartridge, instead (my understanding is) the damage should be calculated individually for each pokemon that is effected by the attack. So if, for example, Regirock uses Rock Slide and first KOes the faster opponent, then spread damage reduction does not occur for the slower opponent, since Rock Slide is now considered to be single-target.
2. On Showdown when a pokemon uses Explosion against two targets, the damage is reduced by the spread damage reduction on both effected pokemon. On cartridge, instead there is no spread damage reduction for the final two pokemon on the field, unlike any other spread damage move. So if, for example, Regirock uses Explosion and its ally Latios uses Protect, then if there is just one target remaining on the field the damage will not be effected by spread damage reduction.
Both of these bugs are demonstrated in this replay:
https://replay.pokemonshowdown.com/gen4vgc2010-1967772555
Turn 1: Rock Slide deals spread-reduced damage to Dialga, which is incorrect.
Turn 2: Explosion deals spread-reduced damage to Dialga, which is incorrect.
Turn 3: Explosion deals spread-reduced damage to Dialga, which is incorrect.
Which corresponds to the twitter link below:
link
1. On Showdown when a pokemon uses a spread attack move, all the damage calculations appear to be done at the start of the attack, however in generation 4 this is incorrect. On cartridge, instead (my understanding is) the damage should be calculated individually for each pokemon that is effected by the attack. So if, for example, Regirock uses Rock Slide and first KOes the faster opponent, then spread damage reduction does not occur for the slower opponent, since Rock Slide is now considered to be single-target.
2. On Showdown when a pokemon uses Explosion against two targets, the damage is reduced by the spread damage reduction on both effected pokemon. On cartridge, instead there is no spread damage reduction for the final two pokemon on the field, unlike any other spread damage move. So if, for example, Regirock uses Explosion and its ally Latios uses Protect, then if there is just one target remaining on the field the damage will not be effected by spread damage reduction.
Both of these bugs are demonstrated in this replay:
https://replay.pokemonshowdown.com/gen4vgc2010-1967772555
Turn 1: Rock Slide deals spread-reduced damage to Dialga, which is incorrect.
Turn 2: Explosion deals spread-reduced damage to Dialga, which is incorrect.
Turn 3: Explosion deals spread-reduced damage to Dialga, which is incorrect.
Which corresponds to the twitter link below:
link
Regirock Attack = 141
Bronzong Attack = 141
Dialga HP = 207, Defence = 140
Rock Slide dealt 23 damage on cartridge
(21, 22, 22, 22, 23, 23, 23, 24, 24, 24, 24, 24, 24, 25, 25, 26) (Single-target)
Rock Slide dealt 19 damage on showdown
(16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 19) (Spread damage)
Explosion (Regirock) dealt 101 damage on cartridge
(94, 95, 97, 98, 99, 100, 101, 102, 103, 104, 105, 107, 108, 109, 110, 111) (Single-target)
Explosion (Regirock) dealt 74 damage on showdown
(70, 71, 72, 73, 74, 75, 75, 76, 77, 78, 79, 80, 80, 81, 82, 83) (Spread damage)
Explosion (Bronzong) dealt 109 damage on cartridge
(94, 95, 97, 98, 99, 100, 101, 102, 103, 104, 105, 107, 108, 109, 110, 111) (Single-target)
Explosion (Bronzong) dealt 73 damage on showdown
(70, 71, 72, 73, 74, 75, 75, 76, 77, 78, 79, 80, 80, 81, 82, 83) (Spread damage)
Also note that the cartridge test was done on HeartGold version on the MelonDS Emulator, this result should be the same for all generation 4 games to my knowledge, however.
Bronzong Attack = 141
Dialga HP = 207, Defence = 140
Rock Slide dealt 23 damage on cartridge
(21, 22, 22, 22, 23, 23, 23, 24, 24, 24, 24, 24, 24, 25, 25, 26) (Single-target)
Rock Slide dealt 19 damage on showdown
(16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 19) (Spread damage)
Explosion (Regirock) dealt 101 damage on cartridge
(94, 95, 97, 98, 99, 100, 101, 102, 103, 104, 105, 107, 108, 109, 110, 111) (Single-target)
Explosion (Regirock) dealt 74 damage on showdown
(70, 71, 72, 73, 74, 75, 75, 76, 77, 78, 79, 80, 80, 81, 82, 83) (Spread damage)
Explosion (Bronzong) dealt 109 damage on cartridge
(94, 95, 97, 98, 99, 100, 101, 102, 103, 104, 105, 107, 108, 109, 110, 111) (Single-target)
Explosion (Bronzong) dealt 73 damage on showdown
(70, 71, 72, 73, 74, 75, 75, 76, 77, 78, 79, 80, 80, 81, 82, 83) (Spread damage)
Also note that the cartridge test was done on HeartGold version on the MelonDS Emulator, this result should be the same for all generation 4 games to my knowledge, however.